1. Field of the Invention
The present invention relates to a furnace temperature detector used in a low-pressure chemical vapor deposition (LPCVD) or a low-pressure thermal treatment process. More particularly, the present invention relates to a furnace temperature detector for detecting a furnace temperature using an overheat thermocouple when an external thermocouple may become defective.
2. Description of the Related Art
Generally, a furnace for fabricating a semiconductor memory device uses various types of thermocouples to control or confirm the temperature of the furnace. An exemplary thermocouple includes an external thermocouple (also referred to as a spike thermocouple), an inner thermocouple, and an overheat thermocouple. To confirm and control the temperature of the furnace, the spike thermocouple shares a single temperature controller with the inner thermocouple.
FIG. 1 illustrates a schematic view of an exemplary furnace. The exemplary furnace includes a reaction tube 1, a heating chamber 3, inner thermocouples 5-1 to 5-4, spike thermocouples 7-1 to 7-4, and overheat thermocouples 9-1 to 9-4. In operation, wafers are reacted with a reaction gas in the reaction tube 1, and the heating chamber 3 supplies heat energy to the reaction tube 1. During operation, the inner thermocouples 5-1 to 5-4 detect the temperature in the reaction tube 1, the spike thermocouples 7-1 to 7-4 detect the temperature of the heating chamber 3, and the overheat thermocouples 9-1 to 9-4 detect an overheating state of the heating chamber 3. In general, a thermocouple is composed of two different metal materials or two different semiconductor materials, which are in contact with each other at two points. Therefore, the thermocouple generates an electromotive force when the temperatures of the two contact points are different. Accordingly, the thermocouple is able to detect a temperature using the electromotive force.
FIG. 2 is a block diagram of a conventional temperature detector for detecting a furnace temperature that includes a temperature controller 14 and an overheat controller 15. The conventional temperature detector of FIG. 2 may be incorporated in the exemplary furnace of FIG. 1. In operation, the temperature controller 14 receives an electric signal (i.e., the electromotive force) from the spike thermocouple 11 (7-1 to 7-4 of FIG. 1) and the inner thermocouple 12 (5-1 to 5-4 of FIG. 1) to generate a temperature control signal TC. The overheat controller 15 receives an electric signal (the electromotive force) from the overheat thermocouple 13 (9-1 to 9-4 of FIG. 1) to generate an overheat control signal OHC.
As shown in FIGS. 1 and 2, in a conventional temperature detector incorporated into an exemplary furnace, the spike thermocouple 11 and the inner thermocouple 12 control the temperature of the furnace, and the overheat thermocouple 13 interrupts the power when the furnace reaches an overheated state. In low-pressure chemical vapor deposition (LPCVD) equipment or low-pressure heat treatment equipment, however, it is difficult to use an inner thermocouple because of the structure of the equipment and due to the characteristics of the process. More particularly, the reaction gas becomes deposited on the surface of the inner thermocouple 12 during the LPCVD process. Thus, it is difficult to detect the temperature of the reaction tube (1 of FIG. 1) accurately.
Accordingly, in a LPCVD process or a low-pressure heat treatment process, the inner thermocouple 12 is used only to profile (i.e., initially check) the temperature of the reaction tube (1 of FIG. 1) before the reaction gas is injected into the reaction tube. Once the reaction gas is injected and the reaction begins, the inner thermocouple 12 is no longer used. In addition, even though the spike thermocouple 11 is attached to the heating chamber (3 of FIG. 1), the spike thermocouple may become damaged when the reaction tube (1 of FIG. 1) is inserted into the heating chamber (3 of FIG. 1) or the reaction tube (1 of FIG. 1) is withdrawn from the heating chamber (3 of FIG. 1). In the event that the spike thermocouple 11 is damaged, an accurate temperature measurement is not taken.
Therefore, due to the damage to the spike thermocouple, the temperature of the furnace may not be measured and controlled accurately. This inability to measure and control furnace temperature accurately may lead to a low yield of the semiconductor devices being formed on semiconductor wafers, which are processed inside the furnace.